Do not generate *.pyc files at all; use /dev/null if possible

Author: fangerer

mx.graalpython/mx_graalpython.py

@@ -1690,7 +1690,12 @@ def build(self):
         mx.ensure_dir_exists(os.path.join(self.subject.get_output_root(), "modules"))
 
         cwd = os.path.join(self.subject.get_output_root(), "mxbuild_temp")
-        pycache_dir = os.path.join(self.subject.get_output_root(), "__pycache__")
+
+        if os.path.exists("/dev/null"):
+            pycache_dir = "/dev/null"
+        else:
+            pycache_dir = os.path.join(self.subject.get_output_root(), "__pycache__")
+
         args = []
         if mx._opts.verbose:
             args.append("-v")
@@ -1700,6 +1705,7 @@ def build(self):
 
         args += ["--python.WithThread",
                  "--python.PyCachePrefix=" + pycache_dir,
+                 "-B",
                  "-S", os.path.join(self.src_dir() , "setup.py"),
                  self.subject.get_output_root()]
         mx.ensure_dir_exists(cwd)